Void context is discussed in many nodes here, like Unhappy returns . Do a 'perldoc -q void", or you can google for "Perl void context". Basically it's pretty complex depending on function and usage, and unless you want to really clutter your mind, just deal with it when you get the warning and give the function a place to put it's return value(s). Read the perldoc for the functions.... ucfirst says it returns a value, map evaluates.